Thermo-mechanical Coupling Nonlinear Vibration And Control Research On Semi-active Hydro-pneumatic Suspension

The hydro-pneumatic suspension has passive and semi-active features because of its strong nonlinear stiffness and damping characteristics,which has been the focus of Chinese and international theoretical research and engineering applications in the past two decades.The studies include nonlinear mathematical and thermodynamic modeling of the oleo-pneumatic separate hydro-pneumatic spring,solving of hydro-pneumatic suspension vibration model and analysis of its characteristics and influence factors,control of semi-active hydro-pneumatic suspension.It has important theoretical significance and engineering application value to improve vehicle comfort and stability.The main contributions of the thesis are as follows:Firstly,a combination of fluid mechanics and Newtonian mechanics is adopted to establish the nonlinear mathematical model of hydro-pneumatic spring.And then the spring mathematical model is built by the power bond graph approach.In addition,the hydro-gas spring performance test bench is developed to verify the correctness of the mathematical model.The results show that the power bond graph modeling method is more accurate,intuitive and easy to use.On this basis,the parameter thermodynamic and thermo-mechanical coupling model of oleo-pneumatic separate hydro-pneumatic spring is set up.And equivalent linearization method is proposed to solution of elastic force and displacement transfer function.Subsequently,the influence of structural parameters on stiffness and damping of the spring is obtained.The heat transfer path of hydro-pneumatic spring is analyzed and thermal resistance network diagram is designed.The simulation equipment of hydro-pneumatic spring environment temperature is developed independently to test working temperature of the spring and the results are consistent with the above theoretical derivation.Thirdly,one quarter of the oleo-pneumatic separate hydro-pneumatic suspension nonlinear vibration model is established and its approximate analytic solution is got by the harmonic balance method and McLaughlin phase combination.Meanwhile,the steady state response of body and wheel displacement is analyzed and the accuracy of the solution is obtained.The rationality of temperature coefficient model is verified and it provides a new way to reduce the vibration of vehicle.Fourthly,the effect of structural parameters,including the wheel stiffness,the spring wire diameter,the middle diameter of helical spring and the initial volume of energy storage device,on the performance of the hydro-pneumatic suspension is analyzed systematically.The expression of the complex stiffness of the oil gas suspension is derived with the consideration of temperature and non negligible temperature.Simulation results show that the change of ambient temperature has a significant effect on the overall stiffness of hydro-gas suspension.And then the influence of the external damping hole diameter on the damping force of the hydro-pneumatic suspension is analyzed in detail,it provides a theoretical support for the research and development of the hydro-pneumatic suspension.Lastly,semi-active control of one quarter of hydro-pneumatic suspension is studied and a new structure for the control of external damping hole diameter by using servo motor is presented.Then the sliding mode control and PID control are used to control the oil and gas suspension damping,the simulation results show that the sliding mode control to the damping is better than PID control.At the same time,it is found that the damping can be adjusted by changing the size of the damping hole,the greater the damping of the hydro-pneumatic spring,the better the suspension vibration isolation effect,the higher the comfort of the vehicle.